Thales’ Theorem in Indonesian Lower Secondary Textbooks

Abstract

Textbooks are an important part in the teaching learning process. However, how
textbooks provide the mathematical content has not been extensively researched. The purpose
of this study is to analyse how Thales’ Theorem is described in scholarly knowledge and
knowledge actually to be taught. I studied five online Indonesian lower secondary textbooks
that are authorised by the ministry of education and four university textbooks. The result shows
how the explanation of Thales’ theorem in the university textbook is different from school
textbooks.